Since other doctors haven’t been able to do anything for him, I would suggest he see a Naturopathic physician.
For the thrush, look for a post on the forum titled “Oral Thrush.”
I would definitely have him go on the Candida diet immediately when he returns home. He should be on the diet for at least a week, then he can slowly add a few antifungal products. You can let us know how he’s doing, someone is always available to talk with you and help when possible.